| 630 | × | 20 100 | + | x | = | ( | 630 | + | x | ) | × | 30 100 |
| Left side of the equation = | 126 | + | x |
| 126 | + | x | = | ( | 630 | + | x | ) | × | 30 100 |
| Right side of the equation = | 630 | × | 30 100 | + | x | × | 30 100 |
| = | 189 | + | x | × | 30 100 |
| 126 | + | x | = | 189 | + | 30 100 | x |
| x | − | 30 100 | x | = | 189 | − | 126 |
7 10 | x | = | 189 | − | 126 |
7 10 | x | = | 63 |
| x | = | 63 | ÷ | 7 10 |
| = | 63 | × | 10 7 |
| = | 9 | × | 10 |
| x | = | 90 |